Friday, 29 August 2014

Bokeh is an effect that pops up in a lot of new games. It is one of those effects that makes a game instantly feel a lot more "next-gen". It is also an effect that usually eats up a lot of performance. For Cello Fortress I came up with a simplified version of bokeh that looks really high quality, is very fast to render and even very easy to implement. My implementation also has some severe limitations, but I think it can work really well for many games.

Bokeh is a part of focal blur, which is also known as depth of field blur or DoF. DoF is the effect that only objects at a certain distance are sharp, while everything closer and further away is blurred. This is an effect that every lens has, and the larger the lens is, the stronger the blur is. Focal blur has been done in many games for quite a while now, but with the normal DoF rendering techniques the bokeh effect is usually lost. Bokeh means that extremely bright spots grow with the blur and appear as clearly recognisable circles (or hexagons or other shapes, depending on the shape of the lens).

The problem with rendering bokeh in games is that a naive implementation requires high dynamic range (HDR) rendering and an extremely large amount of blur samples. HDR has become quite common in games by now, but taking enough samples to get good sharp bokeh is impractical. For bokeh as large as in the image above, you would probably need many hundreds of samples to get it look smooth. I actually tried that exact thing in Proun two years ago, as a fun little experiment.

Proun already had really high quality DoF (as I described in this blogpost). I added bokeh by simply making some pixels extremely bright. This is a quick dirty trick that was needed because Proun only has limited fake HDR, but the effect looks pretty convincing, as you can see below on the left image. However, if the blur is increased the bokeh becomes extremely noisy, as you can see on the right. It looks noisy despite that it already uses a quite insane 128 samples per pixel! You can find more images of this approach in this blogpost.

This makes this naive approach unusable if strong blur is wanted. We need something smarter. The most common approach in current games seems to be to render actual polygons with a bokeh circle texture on them. To do so we need to find all the bright pixels in the image and then generate a quad for each one.

According to this article The Witcher 2 was ahead of its time by having bokeh all the way back in 2011. The Witcher 2 did this by generating a quad for every pixel and then discarding the ones that are not blurred enough. That's a whole lot of sprites to render! Needless to see this only worked in real-time on the very fastest PC videocards.

Most games that have bokeh these days seem to use a smarter approach, using newer shader models: first they look for all the pixels that are so bright that they would get a clear bokeh circle, and then they generate quads for this. An example of this approach can be found here. Unlike The Witcher 2's technique this creates only the bokeh itself, not the general focal blur, so with this technique the depth of field blur needs to be done separately.

Even with this clever technique the performance hit is still heavy. It requires analysing all the pixels on the screen to find the ones that are much brighter than the ones next to it. It also produces temporal artefacts: if the source of the bokeh is really small it will flicker because it is smaller than a pixel. Normally this is not that much of a problem because it is only a pixel, but if a big bokeh sprite flickers on and off this becomes much more noticeable. These temporal artefacts might already show with slight camera movements. I don't know what technique Star Citizen uses, but the kind of flickering this would result in can clearly be seen in this video in the bright spots in the background.

Now that we roughly know how bokeh is usually rendered, let's look at that simple and fast trick that I use in Cello Fortress. My idea comes from that the most pronounced bokeh is often from actual lights, not just random bright pixels. If you are looking directly at a light, but the light is in the blurred background, then it will generate a very clear bokeh circle. In general a game engine already knows where all the lights are, so this means that we can skip the searching for bright pixels entirely and directly create one screen-space quad for every light. To do so I first render the scene, then apply normal depth of field blur, and finally render the bokeh sprites on top of that.

Not only does this method skip the expensive step of finding the bright pixels that need bokeh, it also fixes all the issues with temporal artefacts. We always know exactly where the lights are so no matter how small they are, the bokeh will never flicker when the camera moves. It just moves along with the light correctly.

To get a good-looking effect I scale the bokeh with how blurred the light should be. This can simply be calculated based on the focal settings of the camera and the distance to the camera. I also fade out the bokeh sprite a bit as it gets larger, since the larger the blur, the less bright the bokeh circle should be (unless the light is infinitely bright). Here is a video that shows the bokeh in action in Cello Fortress. The bokeh is mostly visible at the bottom of the screen.

An important part of bokeh is the actual shape of the bokeh effect. This shape is created by the shape of the lens. I often like hexagonal bokeh best, but I recently discovered that in photography this is generally considered ugly. When reading reviews of a new camera lens I wanted to buy I learned that the more expensive lenses have circular bokeh while cheaper lenses have hexagons. Still, in the end the only thing that matters is what looks good aesthetically in your game. Since most bokeh rendering techniques use those textured sprites the bokeh shape can be modified really simply by using a different texture.

Note that this all does not look as good as it can yet because I have so far spent too little time on the actual visual design of Cello Fortress. I mostly focussed on the gameplay and some cool shaders. Once I start working on proper graphics I should also tweak the brightness, size and colour of the bokeh to make it look better. I should probably also try adding a bit of chromatic aberration to the bokeh texture then.

My bokeh technique does not solve occlusion at the moment. If a light disappears behind an object then it should not still get a bokeh sprite. I didn't solve this yet because it does not occur in the current version of Cello Fortress. However, several solutions can be implemented easily. For example, I already have a depth texture for the depth of field blur, so I can do a look-up in that on the screen position of the light to see whether there is an object in front of it.

The big downside of my method for rendering bokeh is that you need to know where the bokeh will appear beforehand. This means that more subtle bokeh sources like reflections and strong speculars are not practically doable. I can imagine some tricks to get for example bokeh in planar reflections working (if you know where the reflecting planes are), but beyond that it quickly becomes infeasible. The standard technique of searching for the bokeh pixels of the image handles this much better, so if you really need bokeh on speculars, then you will probably need to resort to such techniques.

I looked up a bunch of articles on bokeh implementations and couldn't find any mention of something similar to what I am doing. This surprises me because the idea is so simple and obvious. If anyone knows of any articles or games that already do this, then please let me know so that I can add a link.

That's it! My bokeh technique is simpler and much faster than most commonly used methods of rendering bokeh and it even fixes problems with temporal artefacts. It is also a limited technique that does not handle all bokeh effects, but in many cases it will probably be good enough. It definitely is for Cello Fortress!

Sunday, 24 August 2014

Last week we were at Gamescom, showing Swords & Soldiers II and Awesomenauts to the public. Gamescom is the biggest game convention in the world, drawing in a whopping 400,000 people. We have had booths at several conventions in the past years so I figured it might be interesting to share some tips and tricks based on our experiences.

Our booth at Gamescom was part of the Indie Megabooth. The Indie Megabooth is an awesome initiative where a lot of indies hire a big area together and fill it with their games. Since the Indie Megabooth has been so successful in recent years it is now a real organisation with dedicated people to manage it all.

There are several advantages to being part of the Indie Megabooth. For starters it is quite affordable and they take care of a lot of the organisational complexities. More importantly it gives gamers who like indie games a clear spot to go to, hopefully making indie thrive more on a big convention where most booths are gigantonormous monsters from the big publishers. Another good reason to join the Indie Megabooth is that it is great to meet other indies and hang out with them. For example, we were next to Capybara Games, creators of Below, Super Time Force and Sword & Sworcery. Since I really look up to them it was inspirational for me to meet them and discuss game development.

As with all good things there are also some downsides to the Indie Megabooth, in this case mostly because it is so good. The Indie Megabooth is very popular among developers so they get way more requests for booth spots than they can handle. The result is that not everyone can get a booth. It also makes them not very flexible if you want a bigger booth.

To decorate our booth we used big cloth banners. This works really well: they weigh little and unlike posters they hardly tear or damage. You can just roll them up and bring them along. Banners are also a really cheap solution: the type we use costs only around €20 per banner (we got them at Drukwerkdeal.nl). The only downside to the banners we use is that they are slightly transparent, so if the surface behind the banner is coloured or uneven then you might see this through the banners.

The most important thing to us is that as many people as possible get to actually play our games. For this reason we put four screens in our booth: two for Swords & Soldiers 2 and two for Awesomenauts. Since both games support local multiplayer we could have up to ten people playing in our booth. This is quite a lot more than any of the other indie booths, where some could have only one player at a time since they brought just one computer for a single player game. Since players could also play single player on our screens we had between four and ten players at any given time. We rarely had unused computers for longer than a couple of minutes.

While we tried to cramp as many players as possible into our small booth, our friends at Two Tribes had a different approach that I also really liked. They had only two screens for their new game Rive but had a slick design for the booth. They put in nice chairs and beanbags, giving players a very relaxed playing experience. They clearly focussed more on giving each player the best possible experience than on reaching as many players as possible. (Rive is also a great game, by the way, playing incredibly smoothly.)

If audio is important to your game then be sure to bring along some big headphones. There is a lot of noise on game conventions, especially from big booths. We were near an AMD stage where people received free stuff if the crowd shouted "AMD" loudly. At other moments they just played really loud dance music. The Indie Megabooth crew even gave all the indie exhibitors earplugs because of this. One of the other exhibitors had even brought along a microphone to talk to his players without having to shout. When I talked to him it felt quite awkward that he answered me through a microphone while I was right in front of him so I wouldn't personally use this method. Still, I totally understand why he solved the sore-throat-from-talking-loudly-all-day problem this way.

The goal of going to a convention is of course marketing and business. We had a lot of good business meetings and we had many players at our booth, but unfortunately we didn't reach as much press this time as we had hoped. We asked around and most indie devs said the same thing: it was difficult to get a ton of meetings with press going this year. This might be because Gamescom doesn't show as much new stuff as E3, so it is a bit less interesting to the press.

A couple of developers did have a lot of press meetings. One had hired a PR agency to set up the press meetings. While our experiences with PR agencies have so far been very bad, this one had apparently done really well and set up a lot of interviews for them. Another dev said they had started to contact press four weeks in advance. We only started contacting press two weeks before the convention, so we might have also been too late for maximum reach. In general though most devs said they didn't meet as much press as they had hoped, so it seems like Gamescom might also just not be the best spot for this. Of all the conventions we have visited so far we had the most success at Eurogamer Expo a couple of years ago. I have no idea whether that was accidental or whether Eurogamer is actually better for reaching out to press.

From press we go to another exciting topic... utensils! It is a really good idea to bring along a bag of random utensils. My colleague Robin had brought along things like scissors, pins, several types of tape, screwdrivers and pens. Several of our neighbours borrowed them during the convention, so apparently not everyone brings such things along. You never know what might be wrong with your booth so it is good to pack these even if you don't expect to actually need them.

Convention visitors love button badges. They often stick them to their bag right away, hopefully triggering a tiny bit of extra word of mouth and definitely making sure the player remembers the game when he gets home. Buttons are really cheap to order in large batches so we just doled them out freely.

To my surprise our flyers were quite popular. I even saw quite a lot of visitors grab a flyer without playing the actual game.

If you are making a console game then be sure to ask the platform holder for permission to bring along testkits, or borrow special exhibition kits from them for your booth. Travelling with devkits is generally not allowed and you definitely don't want the risk of having to explain to Nintendo, Microsoft or Sony that a devkit was stolen from your luggage... We even got lucky and received two of these awesome exhibition stands from Nintendo. They look really professional and take up less space than a table with a television, so this was really cool.

Really important when exhibiting at a big convention is to never let your booth remain unattended. Always have someone there to look after your stuff. Theft happens a lot at these conventions. The worst time for this is during the night. We knew this beforehand so we brought small computers and carried them to the hotel every evening to be sure they were never left unattended at the booth. Several other indie devs apparently were not aware of this, resulting in two console testkits being stolen from the booths during the night. Never leave stealable stuff at your booth when you are not there, and don't trust convention security to keep your booth safe.

Another tip is to bring a couple of extra people and not have everyone at the booth all the time. Standing at the booth for five days is incredibly exhausting, especially with days like Gamescom's Saturday that last from 9:00 to 20:00. We were with three Ronimo devs and didn't realise until the last day that we could have let one person sleep late every day. This would have helped a lot since getting up at seven every morning and working such longs days is simply too tiresome. Maarten and Robin even had blisters on their feet after a couple of days...

The absolute highlight of being at Gamescom for me were the fans visiting our booth. We met one player who had played Awesomenauts for 2000 hours. Realising that we have made a game that quite a lot of players love so much is incredibly cool! Another player, r0estir0bbe, even brought us a bag of Swiss candy as a gift for the team. Thanks r0estir0bbe! ^_^

Sunday, 10 August 2014

As a cellist, one of my biggest challenges has always been to play notes at the exactly correct pitch. While the keys of a piano and the frets of a guitar make sure that those instruments basically always play notes at the right pitch (as long as the instrument itself is tuned correctly, of course), instruments like a cello and a violin allow the musician to play notes at any pitch, not just at the pitches of real notes. This gives endless possibilities, but it also means that if you put your finger just one millimeter too high or low, it already sounds out of tune and horrible.

Playing in tune has always been a big topic to me, always striving for that oh-so-difficult 'perfect pitch'. Not that I am horribly good at it, but that is exactly why I practice so much to get closer to it. This is why it came as such a shock to me to learn that there is no such thing as 'perfect pitch': several tuning systems exist and they all come with different opinions on what the exact frequency of specific notes should be. They are also all flawed in their own way. Our modern tuning system is called equal temperament and this is not because it allows for perfect pitch, but because it spreads the pain and problems equally everywhere, instead of having some parts perfection and some parts complete horror.

How can this be? Why is there no perfect system for tuning? To understand this, let's have a look at the frequencies of notes in our modern musical system, and how they relate to each other:

Note

Frequency

Difference with
previous note

Percentage higher
than previous note

A

440hz

A#

466.16hz

26.16hz

5.95%

B

493.88hz

27.72hz

5.95%

C

523.25hz

29.37hz

5.95%

C#

554.37hz

31.11hz

5.95%

D

587.33hz

32.96hz

5.95%

D#

622.25hz

34.92hz

5.95%

E

659.26hz

37hz

5.95%

F

698.46hz

39.2hz

5.95%

F#

739.99hz

41.53hz

5.95%

G

783.99hz

44hz

5.95%

G#

830.61hz

46.62hz

5.95%

A'

880hz

49.39hz

5.95%

What you can see here, is that each next note has a higher frequency than the previous, and A' is exactly twice as high as A. This way playing an octave (A and A' at the same time) sounds really good, because their frequencies are exactly double. In fact, it sounds almost like a single note.

What you can also see here, is that the distance between two notes grows the higher we get. This way every time we jump 12 notes for an octave, we get exactly the double frequency. Each next note is approximately 5.95% higher than the previous, so notes are spaced equally when measured relatively.

This all looks fine and dandy, and it is something I have known for years. However, it gets hairy when we look at the distance towards that base note, the A. Note the last column:

Note

Frequency

Percentage above A

A

440hz

A#

466.16hz

5.95%

B

493.88hz

12.25%

C

523.25hz

18.92%

C#

554.37hz

25.99%

D

587.33hz

33.48%

D#

622.25hz

41.42%

E

659.26hz

49.83%

F

698.46hz

58.74%

F#

739.99hz

68.18%

G

783.99hz

78.18%

G#

830.61hz

88.77%

A'

880hz

100.00%

This may look fine, but keep in mind that I previously mentioned that an octave sounds so pleasing because the frequencies are exactly doubled. This goes for other intervals as well. The second-best-sounding interval is at exactly 1.5x the base frequency, so that would be A (440hz) plus E (660hz). However, now look at the table again and note that E is not at 660hz, but at 659.26hz. Slightly out of tune! The same goes for the fourth interval (A+D): the D is not the pleasing 33.33% higher, but the slightly off 33.48%.

This may seem like a tiny difference, but it is actually quite audible, and these aren't even the worst: the major third (A + C#) is at 25.99% instead of at 25%, which is a much bigger difference.

To really understand the problem, you need to hear it. This video explains it quite well by putting perfect chords (50% higher, 33%, 25%) next to the chords of a normal modern instrument (49.83%, 33.48%, 25.99%). Listen carefully to note the difference:

So why don't we fix this up by changing the frequencies to allow for perfect intervals? We could indeed do this, but this would only fix the intervals on top of A. In fact, all intervals would become different depending on what the base note is, because we wouldn't be keeping that 5.95% interval from note to note. No matter how you try, there is no system that results in perfect intervals everywhere. I even tested this with other numbers of notes per octave (instead of the standard 12), but there is no system with perfect intervals.

Letting go of the requirement that all distances are equal, we can choose new tunings that make sure that certain intervals produce perfect chords, while others may sound much worse. This is indeed how tuning worked in the 18th century: some chords sounded perfectly in tune, while others sounded much worse than they do today, making them practically unusable. I guess this explains why baroque music with many sharps or flats is extremely rare: it just doesn't sound acceptable with the tuning used back then.

The system used in the 18th century is called meantone temperament, while our current system is called equal temperament, as all chords sound only a little bit off and none are completely broken. I guess the reason equal temperament replaced meantone temperament is that it allows for much more variation in chord progressions: equal temperament allows all chords in all positions, while meantone temperament only allows specific ones. Those specific ones do sound better though in meantone temperament.

Knowing that the western system with 12 notes per octave is not perfect also explains why other cultures have different numbers of notes. Arabian music for example has 24 notes per octave. This means that in between every one of our notes, they have one extra note. This creates a very different system of musical theory and a very different sound to Arabian music.

Most software for writing music makes it quite difficult to compose with more than the western standard 12 notes, but I have been told that some of the older Prince Of Persia games are notable because the composer abused the MIDI system to play real 24 tone Arabian music. I couldn't find any info on this online though, so I don't know whether that is true.

It is interesting to hear 24 tone music since it sounds quite alien and weird to the western ear, especially when used in a way like this on a special kind of piano:

So why is this all relevant today, now that equal temperament is the golden standard that nearly everyone in the wester world uses? First, it is important to realise that it is not perfect and thus pitch is also not perfect. Comparing a note I play on my cello to one other note might make it sound in tune, while comparing that very same note with another note might result in an interval that is slightly off. This is not because I am playing it wrong, but because the intervals are simply not perfect in our modern equal temperament system.

The second reason this is important to me is that until recently I played in the Kunstorkest, a small amateur orchestra that plays baroque music. Indeed, this is music from the age of meantone temperament, so knowing how it was originally intended is important to us! Not that a hobby musician like myself has the skill to play all the subtleties of this difference, but it helps to at least understand what is going on here and why sometimes the director wants a note played slightly differently. To conclude, here's a short recording of a piece we played with the Kunstorkest: